This project is aimed at characterizing different aspects of the growth and differentiation of transformed melanocytes, a tumor type termed malignant melanoma, including: (1) the host immune responses elicited in tumor-bearing animals and the role those responses play in progressive tumor growth and subsequent metastatic spread; (2) the production of tumor specific proteins, to determine their mechanism of formation and to examine the feasibility of utilizing their specificity for the immunoassay and immunotherapy of melanoma; (3) the role of various cell surface molecules critical to the cascade of events leading to metastatic spread of tumors; and (4) the control mechanisms involved in the regulation of differentiation, i.e. pigment production, in normal and in transformed melanocytes. We have demonstrated that murine melanomas share a common cell surface antigen, termed B700, which elicits tumor rejection; this antigen is related biochemically and immunologically to a normal melanocyte protein, perhaps a differentiation antigen, and is a member of the albuminoid superfamily. We have found that the immune response elicited by B700 is mediated through cytotoxic antibody production, and not through a demonstrable cellular response. We have produced syngeneic murine monoclonal antibodies with specific antimetastatic activity. We have isolated melanoma cell clones which vary in their tumorigenic and metastatic properties, and have employed transfection protocols with the genes for H-2, urokinase, urokinase receptor, and for the H-ras oncogenes, to further elucidate the factors critical to those phenotypes. We have further characterized the molecular controls involved in mammalian pigmentation and its activation by environmental stimuli, employing synthetic oligonucleotide and peptide probes to different pigmentation related gene products. We have shown that mammalian melanin production is regulated primarily through post-translational activation of latent enzyme and the production of a potent melanogenic inhibitor, that multiple gene products are involved in the process of melanin production, and that alternative splicing of mRNA transcripts of those genes are significantly more frequent in transformed melanocytes.